Spectrum Estimation for Low-Load LTE Signals

1. A method, comprising: receiving a signal in a communication terminal; estimating, based on the received signal, a power spectral density that the signal would have under full-load conditions of a transmitter transmitting the signal, by defining multiple hypotheses, each hypothesis specifying a respective set of one or more of time-frequency bins in which the signal is hypothesized to comprise reference signals, measuring a respective received power level of the signal in each of the sets, selecting a hypothesis in which the received power level is maximal, and estimating the power spectral density under the full-load conditions based on the selected hypothesis; and performing an operation in the communication terminal using the estimated power spectral density.

2. The method according to claim 1 , wherein performing the operation comprises searching in the terminal, using the estimated power spectral density, for a Public Land Mobile Network (PLMN) with which to communicate.

3. The method according to claim 2 , wherein performing the operation comprises identifying a Radio Access Technology (RAT) used by the PLMN.

4. The method according to claim 1 , wherein defining the hypotheses comprises specifying the time-frequency bins of the multiple hypotheses in a given frequency sub-band, and wherein estimating the power spectral density under the full-load conditions comprises substituting the measured power level of the selected hypothesis to serve as the estimated power spectral density for the frequency sub-band.

5. The method according to claim 4 , wherein estimating the power spectral density comprises processing the frequency sub-band independently of other frequency sub-bands of the signal.

6. The method according to claim 1 , wherein defining the multiple hypotheses comprises, for a communication protocol that transmits the reference signals in one or more predefined patterns of the time-frequency bins, defining multiple shifts, in at least one of time and frequency, that cover possible shifts of the predefined patterns.

7. The method according to claim 6 , wherein the one or more predefined patterns correspond to respective reference symbol patterns used by transmit antennas of the transmitter.

8. The method according to claim 1 , wherein defining the hypotheses comprises defining multiple time shifts of a predefined pattern of the reference signals, wherein selecting the hypothesis comprises choosing, for each frequency bin, the hypothesis having the maximal received power level for the frequency bin, and wherein estimating the power spectral density comprises substituting the maximal received power level to serve as the estimated power spectral density for the frequency bin.

9. The method according to claim 8 , wherein estimating the power spectral density comprises computing a maximum of the maximal received power level over the frequency bin and one or more neighboring frequency bins, and substituting the computed maximum to serve as the estimated power spectral density for the frequency bin.

10. The method according to claim 1 , wherein receiving the signal comprises receiving a Time Division Duplex (TDD) signal having a period, and wherein measuring the received power level comprises evaluating the power level over at least the period.

11. Apparatus, comprising: reception circuitry, which is configured to receive a signal over a mobile telecommunications air interface; and a processor, which is configured to estimate, based on the received signal, a power spectral density that the signal would have under full-load conditions of a transmitter transmitting the signal, by defining multiple hypotheses, each hypothesis specifying a respective set of one or more of time-frequency bins in which the signal is hypothesized to comprise reference signals, measuring a respective received power level of the signal in each of the sets, selecting a hypothesis in which the received power level is maximal, and estimating the power spectral density under the full-load conditions based on the selected hypothesis, and to perform an operation using the estimated power spectral density.

12. The apparatus according to claim 11 , wherein the processor is configured to search, using the estimated power spectral density, for a Public Land Mobile Network (PLMN) with which to communicate.

13. The apparatus according to claim 12 , wherein the processor is configured to identify a Radio Access Technology (RAT) used by the PLMN.

14. The apparatus according to claim 11 , wherein the processor is configured to specify the time-frequency bins of the multiple hypotheses in a given frequency sub-band, and to estimate the power spectral density under the full-load conditions by substituting the measured power level of the selected hypothesis to serve as the estimated power spectral density for the frequency sub-band.

15. The apparatus according to claim 11 , wherein, for a communication protocol that transmits the reference signals in one or more predefined patterns of the time-frequency bins, the processor is configured to define the multiple hypotheses by defining multiple shifts, in at least one of time and frequency, that cover possible shifts of the predefined patterns.

16. The apparatus according to claim 11 , wherein the processor is configured to define the hypotheses by defining multiple time shifts of a predefined pattern of the reference signals, to choose, for each frequency bin, the hypothesis having the maximal received power level for the frequency bin, and to estimate the power spectral density by substituting the maximal received power level to serve as the estimated power spectral density for the frequency bin.

17. A communication terminal comprising the apparatus of claim 11 .

18. A chipset for processing signals in a communication terminal, comprising the apparatus of claim 11 .